There has been known an engine start-up control device for a vehicle which includes a differential mechanism connected to an engine generating a drive power by combustion of fuel, a first electric motor, and a reactive-force receiving member whose rotation is restricted with a reactive torque controlled by a reactive-force control device. The engine start-up control device for the vehicle has an engine start-up control device for starting up the engine by driving the same by the first electric motor with the reactive-force control device caused to restrict the rotation of the reactive-force receiving member. One example of such engine start-up control device for the vehicle is disclosed in Patent Document 1 (Japanese Patent Application Publication No. 2004-340010). In the vehicle, the engine and first and second motor generators are connected to each other via a differential gear device (differential mechanism), under which the first motor generator starts up the engine by rotatably driving the same. When this takes place, the second motor generator is arranged to restrict the rotation of an output member (reactive-force receiving member) so as to allow an engine rotation speed to vary in a desired profile. In this case, a rotation speed of an output shaft basically depends on a vehicle speed, and the second motor generator, acting as the reactive-force control device, has an effect to supplementarily restrict the rotation of the output member.
In such an engine start-up control device for a vehicle of the related art, however, a battery is limited in charging or discharging at, for instance, under an extremely low temperature, during a drop in charge amount SOC or during a fully charged state of the battery, etc. This causes an output power (power-running torque or regenerative torque) of the first electric motor to be limited, resulting in a delay in rise of an engine rotation speed. Such a structure causes the engine rotation speed to stay for an extended time period in a resonant region (ranging from, for instance, 250 to 4000 rpm) that is determined in terms of rigidity etc. of a power transmitting system. This results in a occurrence of resonance due to torsional vibration of the power transmitting system with a resultant amplified fluctuation of a load torque (rotational resistance resulting from a pumping action and friction) of the engine, causing a risk of uncomfortable shock occurring through an engine mount or the like.
FIG. 13 is a timing chart for a hybrid vehicle shown in FIG. 1 for representing a sequence of cranking an engine 10 for start-up thereof. Under a neutral state in which a power transmitting is interrupted in an automatic shifting portion 20, the second motor generator MG2 (reactive-force control device) allows a rotation speed Nmg2 of a transfer member 18 (reactive-force receiving member) to be maintained at a zero level to receive a reactive force. In addition, the first motor generator MG1 (first electric motor) is rotatably driven for cranking or starting up the engine 10. This timing chart represents a normal state in which output of the first motor generator is unlimited. An engine rotation speed NE is immediately increased due to large power-running torque T1 to escape the resonant region in a short time period, causing no fear of uncomfortable shock arising due to resonance.
In contrast, if the output of the first motor generator MG1 is limited, then, there is a delay in rise time of the engine rotation speed NE by an amount corresponding to a decrease in power-running torque T1 of the first motor generator MG1 as shown in FIG. 25. This increases a time period by that extent for which the engine rotation speed stays in the resonant region. Thus, an amplified fluctuation of the engine load torque Te due to resonance occurs, resulting in the occurrence of uncomfortable shock.
The present invention has been completed with the above view in mind, and has an object to provide an engine start-up control device for a vehicle arranged to suppress the occurrence of uncomfortable shock, caused by engine load torque whose fluctuation is amplified due to resonance because of an increase of time period for the engine rotation speed to stay in a resonant region, when an output of the first electric motor enabled to rotatably drive an engine during start-up thereof is limited.
For achieving the above object, in a first aspect of the invention, an engine start-up control device for a vehicle which includes a differential mechanism connected to an engine generating a drive power by combustion of fuel, a first electric motor, and a reactive-force receiving member whose rotation is restricted with a reactive torque controlled by a reactive-force control device, the engine start-up control device starting up the engine by driving thereof by the first electric motor under a condition where the reactive-force control device restricts the rotation of the reactive-force receiving member. The engine start-up control device is operable to control the reactive-force control device such that in an output limiting state of the first electric motor, a rotation speed of the reactive-force receiving member varies at a greater rate than that in a state where the output of the first electric motor is unlimited.
In a second aspect, in the first aspect, during an engine start-up in the output limiting state of the first electric motor, the reactive torque of the reactive-force control device is decreased to permit the rotation speed of the reactive-force receiving member to vary at the greater rate than that in the state where the output of the first electric motor is unlimited.
In a third aspect, in the first or second aspect, during an engine start-up in the output limiting state of the first electric motor, a torque reference reactive-force control, to control the reactive torque of the reactive-force control device in accordance with a target torque, is executed.
In a fourth aspect, in the third aspect, the target torque is varied such that the lower an output power of the first electric motor in the output limiting state is, the smaller the target torque will be.
In a fifth aspect, in the third or fourth aspect, during the engine start-up in the output limiting state of the first electric motor, a variation amount of the rotation speed of the first electric motor is detected and the target torque is varied such that the greater a rotation speed variation is, the smaller the target torque will be.
In a sixth aspect, in one of the third to fifth aspects, during the engine start-up in the output limiting state of the first electric motor, an in-cylinder pressure of the engine is detected and the target torque is varied such that the higher the in-cylinder pressure is, the smaller the target torque will be.
In a seventh aspect, in the first aspect, during an engine start-up in the output limiting state of the first electric motor, a rotation-speed reference reactive-force control, to control the reactive torque of the reactive-force control device such that a rotation speed of the reactive-force receiving member follows a predetermined target rotation speed, is executed, and a deviation allowable value in the rotation speed of the reactive-force receiving member controlled by the rotation-speed reference reactive-force control is set to a value allowing the rotation speed of the reactive-force receiving member to vary at a predetermined rate.
In a eighth aspect, in one of the first to seventh aspects, the differential mechanism is disposed in a power transmitting path between an output shaft of the engine and drive wheels; and the reactive-force control device includes a second electric motor disposed to give a drive power to the power transmitting path and to receive the drive power from the power transmitting path.
According to the first aspect, the reactive-force control device is controlled such that in an output limiting state of the first electric motor, a rotation speed of the reactive-force receiving member varies at a greater rate than that in a state where the output of the first electric motor is unlimited. Thus, the rotation speed variation of the reactive-force receiving member allows the engine load torque to escape even if the engine rotation speed of which rise is delayed due to the output limitation of the first electric motor stays in the resonant region for a relatively extended time period. This suppresses the occurrence of amplified engine load torque fluctuation caused by resonance due to the torsional vibration of the power transmitting system. Such operation prevents uncomfortable shock from occurring due to an amplified engine load torque fluctuation.
According to the second aspect, during an engine start-up in the output limiting state of the first electric motor, the reactive torque of the reactive-force control device is decreased to permit the rotation speed of the reactive-force receiving member to vary at the greater rate than that in the state where the output of the first electric motor is unlimited. Thus, the rotation speed variation of the reactive-force receiving member, easily occurring against the reactive torque by that extent, allows the engine load torque to escape, thereby suppressing the occurrence of the amplified engine load torque fluctuation caused by resonance.
According to the third aspect, the target torque is varied such that the lower an output power of the first electric motor in the output limiting state is, the smaller the target torque will be. With such a control, for instance, a feedforward control is executed to control the reactive torque at a target torque for keeping the reactive-force receiving member at a predetermined rotation speed (of, for instance, “0” or a speed corresponding to a vehicle speed) in the presence of such a target torque. If the engine load torque exceeds a torque, corresponding to target torque, i.e., a torque determined by a gear ratio, etc., of the differential mechanism, a rotation speed of the reactive-force receiving member is caused to vary against the reactive torque. Such a rotation speed variation allows the engine load torque to escape, suppressing the amplified engine load torque fluctuation caused by resonance.
According to the fourth aspect, the target torque is varied such that the lower an output power of the first electric motor in the output limiting state is, the smaller the target torque will be. Such a structure causes the rotation speed variation of the reactive-force receiving member to easily occur, further effectively suppressing the amplified engine load torque fluctuation caused by resonance. That is, if the output of the first electric motor decreases, the engine rotation speed of which rise is delayed stays in the resonant region for long time period. This increases capability of occurring the amplified engine load torque fluctuation due to resonance by that extent. However, decreasing the target torque for the torque reference reactive-force at a rate depending on the output of the first electric motor allows the rotation speed variation of the reactive-force receiving member to occur with such a small amount of the engine load torque fluctuation. This suppresses the amplified engine load torque fluctuation caused by resonance.
On the contrary, if the reactive torque decreases to cause the rotation speed variation of the reactive-force receiving member to easily occur, then, a rise of the engine rotation speed is interrupted to further delay start-up of the engine. Therefore, it is preferable for the rotation speed variation of the reactive-force receiving member, caused by a drop in reactive torque, to be suppressed to a required minimum level. Thus, a value of the target torque is determined depending on the output of the first electric motor, which appropriately suppresses, with suppressing the occurrence of a delay in start-up of the engine to a minimal level, the occurrence of amplified engine load torque fluctuation caused by resonance.
According to the fifth aspect, during the engine start-up in the output limiting state of the first electric motor, a variation amount of the rotation speed of the first electric motor is detected and the target torque is varied such that the greater a rotation speed variation is, the smaller the target torque will be. Thus, the rotation speed variation of the reactive-force receiving member easily occurs to appropriately escape the engine load torque, thereby appropriately suppressing the occurrence of amplified engine load torque fluctuation caused by resonance. That is, since the variation amount of the engine rotation speed corresponds to the engine load torque fluctuation, an increase of the rotation speed variation means amplification of the engine load torque fluctuation caused due to resonance. Therefore, the target torque for the torque reference reactive-force is decreased at a rate depending on an actual rotation speed variation. Thus, with suppressing the delay in start-up of the engine caused by the drop in reactive torque to a required minimum level, the occurrence of amplified engine load torque fluctuation caused by resonance can be appropriately suppressed.
According to the sixth aspect, during the engine start-up in the output limiting state of the first electric motor, an in-cylinder pressure of the engine is detected and the target torque is varied such that the higher the in-cylinder pressure is, the smaller the target torque will be. Thus, the rotation speed variation of the reactive-force receiving member easily occurs to appropriately escape the engine load torque, thereby appropriately suppressing the occurrence of amplified engine load torque fluctuation caused by resonance. That is, the increased in-cylinder pressure of the engine increases the engine load torque to cause resonance. Thus, by decreasing the target torque for the torque reference reactive-force control at a rate depending on the actual in-cylinder pressure, with suppressing a delay in start-up of the engine caused by a drop in reactive torque to a required minimum level, the amplified engine load torque fluctuation caused by resonance can be appropriately suppressed.
According to the seventh aspect, during an engine start-up in the output limiting state of the first electric motor, a rotation-speed reference reactive-force control, to control the reactive torque of the reactive-force control device such that a rotation speed of the reactive-force receiving member follows a given target rotation speed, is executed, and a deviation allowable value in the rotation speed of the reactive-force receiving member controlled by the rotation-speed reference reactive-force control is set to a value allowing the rotation speed of the reactive-force receiving member to vary at a predetermined rate. Thus, permitting the rotation speed variation of the reactive-force receiving member to occur suppresses the amplification of the engine load torque fluctuation caused by resonance.
Like an eighth invention, an engine start-up control device for a vehicle of the present invention is preferably applied to an electric vehicle, including an engine in addition to first and second electric motors in which either one or both of the first and second electric motors is (are) used as a drive power source for running the vehicle, and the engine is exclusively used for electric power generator or to a hybrid vehicle in which both of the electric motors and the engine are used as a running drive power source. However, the engine start-up control device can also be applied to a vehicle in which only the engine is used as the running drive power source.
For the first and second electric motors for instance, electric motors which are rotatably driven with electric energy, or motor generators selectively rendering functions as the electric motors and electric power generators are preferably used. Depending on a structure, either one of the motor generators may function as the electric power generator. As the reactive-force control device, the second electric motor is preferably employed for instance, but a friction-engaging device (clutch and brake), operative to connect or disconnect (interrupt) a power transmitting path between a differential mechanism and drive wheels, may be used for controlling an engaging torque to control the rotation of the reactive-force receiving member. The engaging torque corresponds to the reactive torque. In addition, both of the second electric motor and the friction-engaging device can be used as a reactive-force control device to control the reactive torque by at least one of them.
As the differential mechanism, although a planetary gear set of a single pinion type or a double pinion type may be preferably used, a differential mechanism of a bevel gear type may also be used. The engine start-up control may be executed during for instance a halt of the vehicle, with controlling the reactive force using the second electric motor under a condition (neutral state etc.) in which the power transfer path is interrupted. In an alternative, the engine start-up control may be executed with controlling the engaging torque (reactive torque) under a condition in which the friction-engaging device of the power transfer path is half-engaged. Even under the running of the vehicle, the engine start-up control may be possibly executed during for instance a shifting of an automatic transmission by interrupting the power transmitting path or by causing the friction-engaging device for the shifting etc. to be half-engaged.
The output of the first electric motor is limited in the following cases. In one case, the output (power-running torque or regenerative torque) of the first electric motor is limited due to a limited a charging or discharging of a battery by for instance under an extremely low temperature, during a drop of charge SOC or during a fully charged state. In another case, the output of the first electric motor is limited due to a failure occurring therein. Under such cases, detecting the limited charging or discharging state of the battery and the presence of such a failure can determine whether to limit the output of the first electric motor. When the output of the first electric motor is limited due to the battery, in a case wherein a target torque is set to a value depending on the output of the first electric motor like a fourth invention, the output of the first electric motor can be acquired by referring to a data map, etc. This data map is preliminarily determined on experimental tests based on for instance a temperature of the battery and the charge amount SOC.
In a second invention, decreasing the reactive torque of the reactive-force control device permits the rotation speed of the reactive-force receiving member to significantly vary. This is because decreasing the reactive torque to a value less than a sharing torque, determined in terms of a gear ratio etc. of the differential mechanism for the engine load torque amplified due to resonance, allows the rotation speed of the reactive-force receiving member to vary. This prevents the engine load torque fluctuation due to resonance from amplifying in a further degree. Accordingly, the reactive torque may suffice to be determined such that the engine load torque fluctuation, arising from resonance, occurs at a magnitude less than a predetermined value.
In a third invention, a torque reference reactive-force control is executed for controlling the reactive torque of the reactive-force control device in accordance with the target torque. This is achieved in feedforward control such that for instance the reactive torque follows or lies at the target torque. The target torque used in such a case may be preferably determined depending on the output of the first electric motor, like the control executed in the fourth invention, but may be preliminarily determined to have a constant value. In the third invention, the torque reference reactive-force control is executed in the output limiting state of the first electric motor. In the absence of the output limiting state of the first electric motor, a rotation-speed reference reactive-force control is executed for controlling the reactive torque such that for instance the rotation speed of the reactive-force receiving member follows or lies at a predetermined target rotation speed. However, the torque reference reactive-force control may also be executed to provide a reactive force at a relatively large target torque. For instance, in the absence of the output limiting state of the first electric motor, the rotation of the reactive-force receiving member may be fixed to “0” or a predetermined rotation speed associated with the vehicle speed, by maximizing the regenerative torque of the second electric motor as the reactive-force control device, or by maximizing an engaging torque of an friction engaging device (reactive-force control device) disposed in the power transmitting path.
In the fourth invention, the lower the output power of the first electric motor is, the less the target torque becomes. In carrying out the third embodiment, a constant target torque may be preliminarily determined regardless of the output of the first electric motor. In addition, when the target torque is determined depending on the output of the first electric motor, a decrease of the reactive torque blocks an increase of the engine rotation speed with a resultant delay in start-up of the engine. Therefore, a predetermined lower limit may be preferably provided on the target torque or an actual reactive torque. This similarly applies to fifth and seventh inventions.
In the fifth and sixth inventions, the target torque may be altered on a real time basis in the course of the engine start-up control. In an alternative, the target torque may be corrected on learning to alter the target torque on subsequent execution of the engine start-up control. In the fifth invention, the variation amount of the rotation speed of the engine is detected to control such that the greater the variation amount is, the lower the target torque will be. In an alternative, the target torque may be lowered in multiple stages or in a continuous fashion depending on the rate or magnitude of the variation amount of the rotation speed. In another alternative, the target torque may suffice to be lowered when it exceeds a certain threshold value of the variation amount.
In the sixth invention, the in-cylinder pressure of the engine is acquired to perform a control such that the higher the in-cylinder pressure is, the less the target torque will be. In an alternative, the target torque may be lowered in multiple stages or in a continuous fashion depending on a level of the in-cylinder pressure. In another alternative, the target torque may suffice to be lowered when the in-cylinder pressure exceeds a certain threshold value. The in-cylinder pressure determined depending on a compression ratio, can be estimated by referring to opening and closing timings, associated with for instance opening and closing signals applied to intake and exhaust valves, the engine rotation speed and an intake air quantity, etc. The in-cylinder pressure, i.e., the compression ratio, is caused to increase at for instance the extremely lower temperature than that appearing at a normal temperature. Moreover, when applied to a flexible fuel vehicle enabled for ethanol etc., to be mixed to fuel at a predetermined mixing ratio, such a mixing ratio is detected to perform, a control such that the higher the mixing ratio is, the higher the in-cylinder pressure will be. Thus, the present invention may be preferably applied to such a vehicle in which the in-cylinder pressure is controlled.
In a seventh invention, the rotation-speed reference reactive-force control is performed to control the reactive torque of the reactive force control device in the feedback control or in a feedforward control depending on the target rotation speed. A deviation permit value may be simply adjusted by altering a gain of for instance the feedback control. Decreasing the gain increases the deviation permitting value. When the upper and lower limit values are set for the target rotation speed to control the reactive torque such that the rotation speed of the reactive-force receiving member falls in such upper and lower limit values, the upper and lower limit values may be altered depending on the deviation permit value. Thus, the present invention may be implemented in various modes.
Upon carrying out the seventh invention, the rotation speed of the reactive-force receiving member is permitted to significantly vary with a structure in which: (a) during engine start-up, the reactive torque of the reactive-force control device is controlled by the rotation-speed reference reactive-force control regardless of the presence of or absence of the output limitation of the first electric motor; and (b) during engine start-up the deviation permit value is set to lie or to follow at a higher value in the presence of the output limitation of the first electric motor, than in the absence of the output limitation. However, such a control in the absence of the output limitation of the first electric motor can be suitably determined. For instance, a regenerative torque of the first electric motor acting as the reactive-force control device may be maximized, or an engaging torque of a friction engaging device (reactive-force control device) disposed in the power transmitting path may be maximized, so that the rotation of the reactive-force receiving member may be fixed to “0” or a predetermined rotation speed etc., associated with the vehicle speed.
In an eighth invention wherein the second electric motor is used as the reactive-force control device, the second electric motor is disposed in the power transfer path between for instance the differential mechanism and the drive wheels, and the engine and the first electric motor are connected to other two rotary elements. In an alternative, the first and second electric motors may be replaced by one another to dispose the first electric motor in the power transmitting path between the differential mechanism and the drive wheels.
During the engine start-up with the output limitation of the first electric motor, performing the rotation-speed reference reactive-force control allows the reactive torque of the reactive-force control device to be controlled depending on the target rotation speed and sets the deviation permitting value so as to permit the rotation speed variation of the reactive-force receiving member. In determining such a deviation permit value, the same control as those of the fourth to sixth inventions can be applied. For instance, (a) the lower the output power of the first electric motor limited in the output limitation is, the greater the deviation permit value becomes; (b) during the engine start-up with the output limitation of the first electric motor, the variation amount of the rotation speed of the engine is detected to perform a control such that the greater the rotation speed variation is, the greater the deviation permit value will be; and (c) during the engine start-up with the output limitation of the first electric motor, the in-cylinder pressure of the engine is acquired to perform a control such that the higher the in-cylinder pressure is, the greater the deviation permit value will be. In these cases, it is possible to obtain the same advantageous effects as those of the fourth to sixth inventions.